p Value

Synonyms

Significance probability

Definition

The p value gives the probability that the null hypothesis is correct; therefore, if it is a small value (like $<0.05$), the null hypothesis is rejected. More technically, it is the probability that the observed data or more extreme outcome would have occurred by chance, i. e., departure from the null hypothesis when the null hypothesis is true. However small, a p value does not indicate the size of an effect. A p value $> 0.05$ does not necessarily mean lack of association. It does so only if there is enough power to detect an association. Most statistical insignificance is due to lack of power to detect an association (poor experimental design).

Cross-References

Statistical vs. Clinical Significance